Photocatalyzed Aerobic Oxidation of Thiols to Disulfides Using Cu₂O Polyhedra

To further demonstrate semiconductor facet effect to photocatalytic organic transformations and address a lack of using simple polyhedral semiconductor particles for disulfide bond formation, Cu₂O cubes, octahedra, and rhombic dodecahedra were used to photocatalyze aerobic oxidation of 4-methylbenzenethiol. After reaction condition optimization, Cu₂O crystals and N,N,N',N'-tetramethylethylenediamine (TMEDA) were added to 4-methylbenzenethiol in ethanol for thiol oxidation to 1,2-di-p-tolyldisulfane under 390 nm light-emitting diode (LED) lamp irradiation for just 5 min. Rhombic dodecahedra gave the highest product yield, followed by octahedra, cubes, and commercial Cu₂O powder. Cu₂O rhombic dodecahedra were subsequently employed to photocatalyze thiols bearing a diverse scope of substituents with satisfactory yields. Reactive species trapping experiments were performed to support a plausible reaction mechanism. Semiconductor crystals with surface control can be a simple but highly effective strategy for enhancing photocatalytic organic transformations.